Oscillation generator of the reflex type



Nov. 22, 1949 w, w, RlGROD 2,489,156

OSCILLATION GENERATOR OF` THE REFLEX TYPE Filed March 9, 1943 13 Z5INVENTOR BY ,umm

ATTOR NEY Patented Nov. 22, 1949 OSCILLATION GENERAP'IOR OF THE REFLEXWilliam W. Rigrod, Bloomfield, N. J., assigner to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication March 9, 1943, Serial N0. 478,560

7 Claims. (Cl. 315-5) This invention relates to velocity-modulatedgenerators and reflector electrodes for electricity of ultra-highfrequency. and more particularly to a special construction of reflectorelectrodes to facilitate the focusing of electron beams.

The primary object of my invention, generally considered, is to providean improved means for adjusting the transit time and controlling thefocusing of electron beams, especially in velocitymodulated generatorsfor electricity of ultra-high frequency, of the type generallydesignated as reflex Klystrons.

Another object of my invention is to provide an improvedvelocity-modulated tube, and especiall,1 one of the reflex Klystrontype, whereby the electron transit time and the focusing of the electronbeam may be more readily controlled.

A further object of my invention is to provide means in a reliexKlystron for focusing the returned electron beam by merely controllingthe potential of an inner element or cylinder disposed between areflector electrode and a resonant-cavity member.

A still further object of my invention is to provide an improved reflexKlystron in which the electron beam may be controlled without changingthe voltage of the reflector electrode.

Other objects and advantages -of the invention, relating to theparticular arrangement and construction of the various parts, willbecome apparent as the description proceeds.

Referring to the drawing illustrating the invention:

Fig. 1 is a fragmentary axial sectional view of a device, of the typegenerally designated as a reflex Klystron, for generating electricity ofultra-high frequency.

Fig. 2 is a transverse sectional view on the line II-II of Fig. 1, inthe direction of the arrows.

Fig. 3 is a fragmentary axial sectional view of a modified reflectorelectrode, associated focusing member, and part of the associatedresonant cavity member, as shown in Fig. 1.

Figs. 4 and 5 are views corresponding to Fig. 3, but showingmodifications.

Fig. 6 is a View corresponding to Fig. 3, but showing a modification inwhich the focusing element between the reflector electrode and resonantcavity member is dispensed with, the shape of the reflector alone beingrelied on for accomplishing the desired purpose.

In the reilex Klystron, electrons in the form of a beam, after beinghunched by passing axially through an electric eld Oscillating atultra-high frequency, enter a region of electric field, which retardsthem until they come to rest and reverse their direction of motion.During this round trip, the differential accelerations and retardationssuperimposed on their motions in the punching process, results in theformation of electron packets which, after reflection, retraverse theultra-high frequency eld at times when that field most strongly opposestheir motion. By suffering deceleration under the action of this eld,the electron packets or bunches give up energy thereto and so sustainits oscillations.

In order to convert the greatest fraction of the electrons kineticenergy into oscillating electric field energy, the direct retardingfield, which effects reversal of the electrons direction, must bedesigned to:

(1) Focus the returning electron beam into the region of strongestoscillating field, and

(2) Retard the electrons at the proper rate so that the bunches are inthe optimum phase relation with respect to said field.

In prior forms of the Klystron, a single reflector electrode has beenused to perform both of the above functions, by varying the voltage (Es)of the resonant cavity member, cavity resonator, or shell and thereflector voltage (Er). The electrode design problem has thus been twiceas diflicult as it would be were a separate electrode used to performeach of these functions.

In accordance with my invention, I propose to use a compound orspecially designed reflector electrode, which desirably includes, inaddition to the reflector member, one disposed between it and theresonant cavity member or adjacent grid, whereby the potential (Ez) ofthis member may be varied independently, as compared with that (Er) ofthe reflector. By applying such a device to a velocity-modulatedbeam-type generator for electricity of ultra-high frequency, such as areflex Klystron, for example, desired results are obtained as follows.

An advantage of using such a compound reflector lies, not only in itssuperior versatility as 3 compared with a single electrode, butprincipally and specifically in its ability to control the focusing ofthe returned electron beam and its transit time, that is, its relativephasing as compared with radio-frequency voltage, independent of 5 eachother.

If the potential of the shell or resonant cavity member is regarded as100 and that of the reflector as 0, then it has been foundexperimentally that radio frequency power output was obtained from areflex Klystron, equipped with a compounds reflector.U embodying.v myinvention; when the .zpotential "ofathe associated' member; such as aninner cylinder disposed between the one or more leads or supports 35 forelectrode means, such as an associated control electrode 36, here shownas hollow cylindrical, which with associated insulating material 3lbetween it and a generally cylindrical rim portion of said electrode 34,form a compound reflector device or electrode embodying my invention.The insulating material 31 divides the compound reflector electrode intoa plurality of insulated zones, the spherical portion of the electrode34, or second zone, being arcuate about the aXis of the opening in thesurfaeeeofnther electrode S31-:considered as. the first zonen As`sthesdi'ameterf.ofthe opening" in the control electrode 35 is less thanthat of the elecreflector and shell, lay in the range between 0andlsstmde 34, the surface of the compound reflector 19. Theequipotential surface at which electrons reached zero velocity before:starting back in theopposite direction was in the range between `V and35, that is, always positive with respect to the associated member orcylinder:

Thus, the turn-about positions forfthenelectrons end-plate or grid,showing that focusingzof--the electrode, subtends about a point in itscentral region,V asolidiangle substantially greater than Z'ir solidradians.

Whensin operation," a beam of electrons from zthesproperlyrorientedcathode I2 passes successiveiywthrough i the f openings, intermediatethe electronebeam-.projecting means I2 and the reiiector electrode,le'ft by the grids I'I, IB and 23, and-Histurned back, before reachingthe reector returned beam depends entirely on the potential 34, at theequipotential `surface in accordance of saidcont-roLmember relative ytothe. shellpotenel` tial.

Itwasfound-that best results couldbe obtained, forvjav. given: reiiector.-,potentiaL .when theinnerf tial. positive with. respect tothereflector cup for.-

allnvalfues.0f..shell.voltage.. This Ais an important?.l practicaladvantagenfonmy compound reflector-,-,

asfor any singlernode of operation the compound/.I

refiector:x requires: nos more adjustment than a .35t..}tentia1singleelectrode.

Referring L-now .toy` thel drawingsr VinV detail, like e partssbeing gdesignated. .by =like reference l charaoters, andorst considering theembodimentof..

myinvention illustratedin Figsfl and12, there fis. y

shownuahportion..offa reflex'llystron II com@ prisingfan.electronfemissive cathode 4I2 supported" inside of an envelope portionI3, only-fragmen.- tani'ly ,1 illustratedl Said envelope `portionhas sacollanfor outstanding-.;annular angemember I4--45V52 extending, from.its..periphery,. and at.-.one endo partly closedby grid-support memberI5 having,-

a collar I6 providing an opening furthe passageffof.electrons...and..toewhich `grids. I'I eandvrl :are secured.

n) Thaupper portion', of the collar `-I 6 -denes ythe interior portion.ofVA the.- .cavity `resonator orshell: member I 9, secured r`thereto#by 4means-fof? atflexe, ible. diaphragm. or..lo.wer-wall portion: 2|..The

remainderpf Ithe resonator `member .consists of..v 1

in.. fthe present embodiment,,projects a coaXiaL- I output memberorantenna. 255.F Mechanical ktun.-l ing. or ,adjustmentof .the resonantcavity. `may Ybe eected .by turningaplurality of screws 26.to flex..

theamember: 2.Ldto.ai greater `orlesser extents.

{35.trolledf in any desired manner; as from' the-sameH against..theyresistaneeof the-tension coil springs.

21,; acting, betweenthe flange. member.. I4 and .aM

correspondingflange ,member 2.\to whichv the upper. wallportion.22:.andthe cylindrical...wall

portion24arewseeured, asibymeansxof solder 29..

Projecting axially firomi the flange .f member..28..f70 L;

is .:a..sleev.e..member 3I-,closed atv itswouter: or upper,endbya.flaremember 32,4 yof glass or... other vitreous material, through: a press.--,of Whichnpass .af-rod or` support. 33k for areectorwithsthevelocity;-thereof.v The equipotential surfaces:arefnot'shetchedin Fig;l l, but correspond-1n inglsurta`ees-f38fand '39 are-,shown inFig. 6.- Anf electron :having -a relatively slow velocity may be@ or`control:member waskept at. alconstantpoten- A30V.re-lectedfatfarelatively. high potentiar surface-1.

corresponding; for example, withthe-one-desi'gnatediasx,Whilefarelatively fast Lelectron maypenetrate'fsuch:surface fand nally be reflected-at.'y

a ysurtac'e such i as -3 9 Vhaving a more negative' po`v reflect all ofthe electrons back into the shell-orv resonaton'device and. avoidundesired Vdispersion thereof.

Fig'al .alsoillustrates'a wiring ,diagram which Inany -event-,.however,the yreflector sur`^ face willlxbefconcaveyor'of such acharacterasto.,V`

mayrbe usedfrinl the. operation offlthe generator.

The i-cathodefi 2,." forexample, may be heated by".

energy'ffrcm; an] adjustable transformer `l I `the primar-y:winding-"5421off-whichfis'connected to a suitable'esource-ofripower andthe secondary windingfllsoffwhichds connected to-the heating` The shellor res-- lament. IIIIIy :of: fthe -cathode.- onant cavity member I9,desirably groundedas.

tialnbeingfindicated bythe` movable arrow 46.

ode.;I2,-;.asnbymeansfof abattery 4l or other V'Ikhefreector-member.3sis maintained at a negiative potentialrxEr) witnrespeet to thel shellmember I9, as wellas withzrespecttothe cathsource of direct current,adjustability being. in-

`ydicatedtby.theumovable arrow 48.. The1potenftial of the .controlelement 33., in-this. case shown hollowe'cylindnical, `andat a potentialpositive` with respect to the reflector lkrandlintermediate that:ofsaidreflectorfand the resonator I9, is conbattery-"IIIeby means of themovable -or adjustable meansor connecting member 49.l The cathode shield53 is..maintainedat. a .relatively small positive potential withrespecttothe. cathode. I2,.by.

lbatteryorl other .source of direct current. 54.

If' the eleetrode`f34'ffhere rshown; generally spherical,andinaapotentiaMEzh` oi.- the-,.cylindrcal` control member- 3B is keptconstant, however, the field lines near its mouth will be essentiallyunchanged.

Thus I have found experimentally that with the potential differencebetween the reflector member 34 and the cylindrical member 36 fixed atany one of a number of optimum values, the reflector potential (Er) forany one of a number of modes in each case remained essentially constantfor best output, as the shell voltage (Es) varied over a wide range.This potential difference, Eb=ErEa Thus for each value of the innercylinder voltage (Ez), the compound reiiector of the shape depicted inFigs. 1 and 2 can be regarded as a single deep concave reiiector, of acorrespondingly adjusted depth, while having the same mouth diameter andgeneral shape.

The following table shows typical operating data for a reflex Klystrenwith a compound reector, as in Figs. 1 and 2.

R t PositiveI Volt- R F e ec or age on nner Shue gom Cup Po- CylinderRelg tential E, ative to Rewatts) Hector Cup El,

Another desirable configuration for a compound reiiector, correspondinggenerally with that shown in Fig. 1, is illustrated in Fig. 3, in whichthe reflector member proper is designated 34*l while the focusing orcontrol member is designated as 3Z-y ,the adjacent grid of the resonantcavity member 19a being designated as 23a. The members 34gq and 362L maybe held together by suitable insulation (not shown), as in Fig. l. Inthe present instance the reflector member 3Aa is not only shapedsomewhat differently, but the control member 36E is hollowfrusto-conical rather than cylindrical.

Referring now to the embodiment of my invention illustrated in Fig. 4,the reflector member is here designated by the reference character Sb,while the associated control member is designated as 36h, the grid ofthe associated resonant cavity member lb being designated as 23h. Inthis case, the reflector member is like a hollow cylinder of short axiallength and closed at only one end, while the control member 36b is likea surface of revolution, somewhat frusto-conical except that it curveslongitudinally as well as circumferentially.

The embodiment of my invention illustrated in Fig. involves a reiiectormember 34C, somewhat like the reiiector 34EL of Fig. 3, and a controlelectrode 36C in the form of a fiat plate with an opening 5l of adiameter less than that of the mouth of the reflector member 34c but,like the corresponding openings of the other forms, at least as large asthe adjacent resonator opening or grid. The associated resonator isdesignated by the reference character |90, the adjacent grid thereofbeing 23.

In designing single electrode reflectors for reflex Klystrons, the chiefconsideration has been to obtain the maximum power conversion effl- 6 lciency in producing radio-frequency oscillations. The result has been,in most commercial models, a shallow cylindrical cup, whose base isgiven a slightly concave curvature facing the cathode.

In some Klystrons the radio-frequency power output tends to decreasesharply with slight deviations of the shell or beam-accelerating voltage(ES) from its optimum value. However, a fairly broad range of shellvoltage can be used without sharp decline in power output, providing thereflector voltage (Er) is readjusted at each successive change in shellvoltage. This adjustment of reiiector potential to get maximum poweroutput, for any value of shell voltage, is fairly critical.

It is clearly an improvement, increasing ease of operation andmaintenance, if a reflector is used so that one of the two voltages (Esand Er) can be varied over a wide range without greatly affecting theradio-frequency power output of the oscillator. Anembodiment of such areflector is illustrated in Fig. 6 and designated by the referencecharacter 34d. When using such a reflector in a Klystron, as illustratedin Fig. 1, the shell potential may be varied over a range of more than500 volts with a constant reflector voltage (Er) with sustained maximumradio-frequency power output.

'Ihis means that, in addition to maintaining good electron-beam focusing.over this range of (Es), the reflector configuration also gave rise toapproxi-mately constant transit time for the corresponding range ofpenetration distances of electrons into the reiiector region, @withunchanged voltage Iapplied to the reflector.

The essential features of my reflector, illrustrated in Fig. 6 are:

(l) Cylindrical rim :portion close to the outer surface of the adjacentWall of the resonator member (ld) producing an equipotential fieldcontour of high curvature, as shown lby the dotted lines designated 38and 39, and in terms of electron optics, short focal length.

(2) The `depth of the remaining or generally spherical portion of thereflector cup 34d is shown approximately as great as the radius of itsmouth. The bottom need not be spherical, as illustrated, but can be flator otherwise formed, its shape having little effect on the equipotentialsurfaces lat which the electrons come to rest and reverse directions, asthese surfaces are close to the mouth of the cup, due to the high iieldconcentration there. The depth of the cup is necessary to permit theseequipotential surfaces to assume vthe desired shapes, such thatelectrons penetrating to desired distances are returned in a beamfocused t0 approximately the same position on the tube axis between thecavity grids.

Another way of regarding this operation is to consider the reflectingequipotential surface as lan electron-optical mirror. Inasmuch as anytransverse force acting lon an yelectr-on changes its direction .ofmotion most greatly when the electrons velocity is least, theelectrostatic forces :acting on the electrons when they come to rest aremost important in determining their return zpath. Thus the equipotentialsurfaces in the neighborhood of the turn-about position must have focallengths which are roughly 'proportional to their distances from theregion .between the two cavity grids, in order that electrons of a largerange `of entrance velocities will .be returned and refoc-used vat thatposition. This is shape illustrated in Fig. 6.

In general, variations of the shell voltage changes the qualltyof `theradio-frequency output-by altering both` its magnitude land itsirequency. In the-former design of Klystron, any changein the shellvoltage must be accompanied by a-corresponding' change inthe reflectorvolt'- afge tofmaintain :approximately constant transit time and sosustainoscillations. By using either the single orfcompound reflectorembodying my invention, both of' these variations in output may beei'ectedby changing only one voltage, namely, that' of the shell. Forexample, increasing the shell voltage', increases the frequency, andvice versa.

From the foregoingfit-will be seen that I have devisedareflector'device,v which may :take either theforin iota compoundlorplural voltage refleet-or, or that-of la' single deep reflector, to1facilita't'e the vadjustment of the transit time and control the"focusing of the electron beam in ,a generator of ultra-highIfreq-uency. The control of amplitude `andfrequency may be effected bymerely varying the shell voltage, once the potentials=of theelectrodeelements have been pre-set for a` desiredrangeof' operation. Inaccordance with myV invention .the precision and flexibility inpre-settingthedesired mode of operation may be vastly increased'byusing` a plurality of reflector elements-held.. at different potentialsin place of ione, -to--perform individually the `two distinct:functionsfpreviously required of :the one.

Although :preferredembodiments of my invention` haver been disclosed, itwill be understood that'modications imay kvbe `made within the spiritvand scope oftheappended claims.

l. A velocity-modulated high-frequency generator of theireex typecomprising an electronemissive cathode, a cavityv resonator adjacentthereto, a reflector electrode toward which the output of said-cathodeis directedl and disposed onfthe side offsaid'resonator opposite fromthat of said cathode, Aelectrode means disposed intermediate said4reflector electrode and resonator, means vincluding asource-of voltageand conductors connected between -saidlsource f and vsaid resonator,said--reilector electrode, and said electrode means, for maintainingsaid resonator at a high positive :potential with respect to saidcathode, said reilectorelectrode at a negative potentialwwith respect tosaiducathode, and said electrodermeansatI a potential intermediate thatof theresonatorand said reilector'electrode, in order. tocontrolthefocusing ofthe electron beam returned bysaidreflector electrode.

A2. A ,reex-Klystron comprising an electron-- emissive...cathode,.aA'cavity resonator associated therewith, a reflector. electrode disposedon one side ofcsaidresonator opposite that of said cathode said.electrode `'having a, reflecting surface shapedgenerally like' aportionA of asphere open- 81 ing axially ofthe 'Klystron, a cylindricalrim portion disposed coaxially therewith, partially closing the mouththereof, and extending therefrom close to said resonator, for producingan electric eld contour of high curvature, lead-in means from saidcathode, resonator, rellector electrode, andl cylindrical riml portion,and sources of potential connected to said lead-in means for maintainingsaid cylindrical rim portion positive with respect to said reflectorelectrode, but still negative with respect to said resonator, in orderto control the focusing of the electron-beam returned by said reflectorelectrode.

3. In an oscillation generator of the reflex type, a cavity resonator'having an opening in each of opposite Iwalls, means for projecting abeam of electrons through said openings, a reilector electrode disposedon the side of said resonator opposite Ito that of said projectingmeans, formed with a concave generally spherical surface adjacent saidresonator and aligned with the openings, and an electrode member, formedhollow for the passage of the electron beam, partially fenclosed in saidreflector electrode, disposed ;coaxially of said generator, positionedbetweeniand insulated from said reilector electrode and resonator, andhaving an opening adjacent said resonator at least as large as theadjacent resonator opening. A

4. A cavity resonator having a pair of openings in its Walls, means forprojecting a beam of electrons through said openings and a reectorelectrode aligned `with said openings and comprising a hollow memberhaving conducting wall portions subdivided into a plurality of insulatedzones, said openings being intermediate the means and the reflectorelectrode,and adjustable means connected to said zones for varying atwill independently for each of the zones the relative electricalpotentials of said zones and said resonator.

5. A reflector electrode for an oscillation generator of the reflex typecomprising a hollow body having a surface of conducting materialsubdivided into a plurality of Zones insulated from each other, andhaving an opening in the surface of a first one of said zones, a secondone of the zones having an inner surface arcuate about the axis of saidopening.

6. A cavity resonator having a pair of openings in its Walls, means forprojecting a beam of electrons through said openings and a reflectorelectrode aligned with said openings and comprising a hollow memberhaving conducting wall portions subdivided into a plurality of insulatedZones, said means being oriented relative to the openings and theelectrode to project said beam through the openings toward the reflectorelectrode, and adjustable means connected to said zones for varying atWill the relative electrical potentials of said zones and saidresonator, the surface of said reilector electrode subtending, about apoint in the central region of said reflector electrode, a solid anglesubstantially cgreater than 21r solid radians,

7. In an oscillation generator of the reflex type, a cavity resonatorhaving aligned openings, means for projecting a beam of electronsthrough said openings, a reilector electrode disposed on Ithe -side ofsaid resonator opposite to that of said vprojecting means,aligned withthe openings, and presenting to said resonator a cup-shaped surface,andan electrode member, Ainsulated from, and partially bridging the gapbetween, said reflector electrode and resonator, formed with an WILLIAMW. RIGROD.

REFERENCES crrnn The following references are of record in the 111e ofthis patent:

UNITED STATES PATENTS Number Name Date Henneberz et al. June 27, 1939Number Name Date Cage Feb. 13, 1940 Varian v.. June 17, 1941 Varian etal. July 29, 1941 Hansen et al. Oct. 21, 1941 Linder Mar. 17, 1942Morton Mar. 31, 1942 Linder Aug. 18, 1942 Harrison et a1 Jan. 21, 1947Hill Mar. 18, 1947

